Sensing the value of environmental parameters such as temperature and strain using an optical fiber with a plurality of fiber Bragg gratings is known. For example in U.S. Pat. No. 4,996,419 there is disclosed for sensing strain a multitude of separate longitudinally spaced Bragg sensing gratings of substantially equal initial periodicity for all of the sensing gratings, each of the sensing gratings being situated at a different one of a multitude of separate locations.
During certain procedures, such as hyperthermia therapy a surgeon needs to know the temperature profile in the tissue at and near the area under treatment. A number of techniques and technologies are in use or being investigated for temperature sensing in conjunction with hyperthermia therapy. In one such technique the temperature at different locations is determined by inserting a cannula in the area under treatment, and by inserting a single point temperature sensor into the cannula. The point temperature sensor is moved within the cannula to different locations for reading temperature. Such a procedure is laborious, and of uncertain precision because of the need to relocate the point sensor for each measurement at each of closely spaced locations. Moreover, the temperature profile determined in this manner is not totally reliable and is not obtained simultaneously for the succession of locations. Another technique is the use of several point sensors separately connected and placed.
The need for temperature profiling occurs, for example, in cancer treatment when a tumor is to be heated during hyperthermia treatment. In this case, the tumor is to be heated, for example, in the range 41-45° C. (up to 113° F.), while the surrounding tissue is to be maintained at lower temperatures to avoid damaging healthy tissue.
Although hyperthermia therapy is under use and investigation for cancer, it is understood to be useful for other treatments. One such treatment is for BPH (benign prostatic hyperplasia).
As far as is known at present, different hyperthermia therapies employ different temperature ranges. For example, in investigational work with whole body hyperthermia a range of 40-42° C. is employed. In hyperthermia therapy to sensitize cancer cells to the effects of other therapies such as radiation therapy, chemotherapy and biological therapies, localized heating to temperature in the range of 41-45° C. have been used. Other techniques are used to achieve much higher temperature in order to ablate the tissue being treated. These techniques have been investigated in the brain, liver and prostate and require very precise placement of the energy in the tissue that needs to be ablated. In all types of hyperthermia therapy, temperature monitoring is critical.
Body tissue temperatures as high as 45° C. (113° F.) have been used in hyperthermia therapy. The effectiveness of hyperthermia therapy is related to the temperature achieved and other variables. In this regard it is important that the desired temperature is reached, but not exceeded. To accomplish this the temperature of the tumor or the area targeted for treatment and surrounding tissue most be closely monitored. Therefore accurate in vivo temperature monitoring is necessary, not only at the point or area under treatment but also at adjacent tissue. Also, for several of the heating methods, such as by microwave radiation, sensor immunity to electromagnetic fields is required. Consequently, it would be advantageous to provide a temperature profiling system and method that can measure temperature simultaneously (or nearly so) at a number of closely spaced locations, and that can do so repeatedly over short time intervals. Also, small changes in temperature should be made available over time intervals to measure change in temperature
In certain hyperthermia applications the sensor must be able to measure discrete points over a short distance and the measuring points being as very close together. For example, the total distance may be 5 cm, with 10 measuring points. Typical hyperthermia treatment is applied to tissue areas spanning a length of about 1 cm-5 cm. Consequently in order to measure temperature at a plurality of point along such a distance very short fiber Bragg gratings must be employed. Also, in some hyperthermia applications it is desirable that each measuring point have a temperature resolution of at least 0.1° C. It is also desirable that the several measuring points provide sufficient spatial resolution that the temperature at one point does not overly influence the temperature reading at adjacent points, even if the measuring points are very close together. The invention in its various aspects and according to its principles address these requirements.